Negative Active Material, Method of Preparing Negative Active Material, Negative Electrode Including Negative Active Material, and Rechargeable Lithium Battery Including Negative Active Material

This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0048823 filed in the Korean Intellectual Property Office on Apr. 11, 2024, the entire contents of which are incorporated herein by reference.

Embodiments relate to a negative active material, a method of preparing the negative active material, a negative electrode including the negative active material, and a rechargeable lithium battery including the negative active material.

With the rapid spread of electronic devices that use batteries such as mobile phones, laptop computers, and electric vehicles, a demand for smaller, lighter, and relatively high-capacity rechargeable lithium batteries has rapidly increased. Improving the performance of rechargeable lithium batteries has therefore been considered.

Rechargeable lithium batteries include a positive electrode and a negative electrode including an active material capable of intercalating and deintercalating lithium ions, and an electrolyte solution. Electrical energy is produced by oxidation and reduction reactions when lithium ions are intercalated/deintercalated at the positive and negative electrodes.

One or more embodiments provide a negative active material exhibiting high-capacity, high efficiency, and excellent cycle-life characteristic.

Another embodiment provides a method of preparing the negative active material.

Still another embodiment provides a negative electrode including the negative active material.

Still another embodiment provides a rechargeable lithium battery including the negative active material.

One or more embodiments provide a negative active material including a core including a porous support including pores; a carbon layer provided in the pores, a silicon layer provided on the carbon layer; and an amorphous carbon layer provided on an outer surface of the core, wherein the pores include mesopores that are about 50% to about 100% of a total porosity of the porous support.

Another embodiment provides a negative active material including secondary particles that are an agglomeration of primary particles; wherein the primary particles include (i) a core including a porous support including pores, (ii) a carbon layer provided in the pores, (iii) a silicon layer provided on the carbon layer; and (iv) an amorphous carbon layer provided on an outer surface of the core, wherein the pores include mesopores that are about 50% to about 100% of a total porosity of the porous support.

Still another embodiment provides a method of preparing a negative active material including first vapor coating on a porous support including pores with a carbon gas to form a carbon layer in the pores; second vapor coating on the carbon layer with a silicon gas to form a silicon layer; and coating an outer surface of the porous support with an amorphous carbon precursor, wherein the pore include mesopore that are about 50% to about 100% of a total porosity of the porous support.

Still another embodiment provides a rechargeable lithium battery including a negative electrode including the negative active material; a positive electrode; and an electrolyte.

A negative active material according to one or more embodiments may exhibit excellent charge and discharge efficiency, high-rate characteristic, and excellent cycle-life characteristic.

Embodiments are described herein in detail. However, the embodiments are exemplary, and the present disclosure is not limited to the disclosed embodiments.

Terms used in this specification explain embodiments but are not intended limit the full scope of the present disclosure. Expressions in the singular include expressions in plural unless the context clearly dictates otherwise.

The term “combination thereof” may include a mixture, a laminate, a complex, a copolymer, an alloy, a blend, a reactant of constituents.

The term “comprise”, “include” or “have” are intended to designate that the performed characteristics, numbers, step, constituted elements, or a combination thereof is present, but it should be understood that the possibility of presence or addition of one or more other characteristics, numbers, steps, constituted element, or a combination are not precluded.

The drawings show thicknesses enlarged in order to clearly show the various layers and regions, and the same reference numerals are given to similar parts throughout the specification. If an element, such as a layer, a film, a region, a plate, or the like is referred to as being “on” or “over” another part, it may include cases where it is “directly on” another element, but also cases where there is another element in between. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

Herein, “layer” includes a shape totally formed on the entire surface or a shape partial surface, when viewed from a plane view.

Herein, “or” is not to be construed as an exclusive meaning, for example, “A or B” is construed to include A, B, A+B, and the like.

As used herein, when a definition is not otherwise provided, a particle diameter or a particle size may be an average particle diameter. The average particle diameter indicates an average value of the diameter of the particles depending on a cumulative volume in the particle size distribution of particles included in the negative active material. The average particle size (D50) may be measured by a method well known to those skilled in the art, for example, by a particle size analyzer, or by a transmission electron microscopic image, or a scanning electron microscopic image. In some embodiments, a dynamic light-scattering measurement device is used to perform a data analysis, and the number of particles is counted for each particle size range, and from this, the average particle diameter (D50) value may be easily obtained through a calculation.

The particle size may be measured by a laser diffraction method. The laser diffraction may be obtained by distributing particles to be measured in a distribution solvent and introducing it to a commercially available laser diffraction particle measuring device (e.g., MT 3000 available from Microtrac, Inc.), irradiating ultrasonic waves of about 28 kHz at a power of about 60 W, and calculating an average particle diameter (D50) in the 50% standard of particle distribution in the measuring device.

In some embodiments, an average particle diameter may be measured by various techniques such as, for example, by a particle analyzer.

In some embodiments, a thickness may be measured by a scanning electron microscope (SEM) or a transmission electron microscope (TEM) image for the cross-section. But the present disclosure is not limited to thickness measurement by SEM and TEM, and thickness may be measured by any other techniques known in the related arts. The thickness may be an average thickness.

As used herein, soft carbon refers to graphitizable carbon materials and are readily graphitized by heat treatment at a high temperature, e.g., about 2800° C. Hard carbon refers to non-graphitizable carbon materials and are not substantially, and not slightly graphitized by heat treatment. The terms soft carbon and hard carbon are well known in the related arts.

In some embodiments, the crystalline carbon and the amorphous carbon may be distinguished through X-ray diffraction (XRD) measurement. The crystalline carbon includes natural graphite and artificial graphite. Natural graphite may indicate graphite that may be naturally generated by separating it from minerals, and if measured by XRD, the interplanar spacing (d002) of the (002) plane may be about 3.350 Å to about 3.360 Å. Artificial graphite may indicate graphite manufactured by graphitization, and if measured by XRD, the interplanar spacing (d002) of the (002) plane may be about 3.355 Å to about 3.365 Å. The amorphous carbon may have the interplanar spacing (d002) of the (002) plane of about 3.34 Å or less, if measured by XRD. The XRD may be measured using CuKα ray as a target line with an X-ray diffraction analyzer (e.g., product name: X'Pert, manufacturer: Malvern Panalytical) and by removing a monochromator to improve a peak density resolution. The measurement condition may be 2θ=10° to 80°, a scan speed (°/S) of 0.044 to 0.089, and a step size (°/step) of 0.013 to 0.039.

A negative active material according to one or more embodiments includes a core including a porous support, a carbon layer positioned in the pores, and a silicon layer positioned on the carbon layer; and an amorphous carbon layer on an outer surface of the core, wherein the pores include mesopores and a porosity of the mesopores is about 50% to about 100% based on 100% of the entire porosity.

schematically shows the negative active material according to one or more embodiments. As shown in, the negative active materialincludes a core including the supportincluding pores, a carbon layerpositioned in the pores, a silicon layerpositioned on the carbon layer, and an amorphous carbon layerpositioned on the outer surface of the core. In, P indicates pores before forming the carbon layerand the silicon layer. The size on the left ofschematic illustrates the size of pores.

The support according to one or more embodiments is formed with pores, and the pores have various sizes such as micropores, mesopores, or macro pores. Among these, the mesopores are included at about 50% to about 100% of the total porosity. The mesopores may have an average diameter of about 1 nm to about 50 nm. In one or more embodiments, micropores indicate pores having an average diameter less than about 1 nm and the macropores indicate pores having an average diameter greater than about 50 nm.

The mesopores may constitute about 60% to about 100%, or about 70% to about 100% of the total porosity. The average diameter of the mesopores may be about 1 nm to about 50 nm to allow for the silicon to be positioned in the mesopores. Accordingly, as silicon with the average diameter of about 1 nm to about 50 nm is positioned within the pores of the porous support, volume expansion of the silicon may be inhibited, and silicon with the average diameter of about 1 nm to about 50 nm may be appropriately included in the negative active material in proportion to a percentage of mesopores. If the mesopores are less than about 50% of the total porosity there may be an insufficient region for deposition of the silicon, and, thus, the designed capacity may be not realized.

The entire porosity of the porous support according to one or more may be about 30% to about 90%, about 40% to about 80%, or about 50% to about 70%. If the entire porosity of the porous support is within these ranges, the silicon may be included in the pores at the sufficient amount, thereby exhibiting a much higher capacity.

The entire porosity and the meso porosity of the porous support may be measured by a Barrett-Joyner-Halenda (BJH) method. For example, the porosity may be determined by measuring the pore volume by using a BJH method through Nabsorption isotherm and dividing the measured pore volume by the volume of the entire porous support. In detail, the porous support is pre-treated by increasing a temperature to about 523 K (Kelvin, absolute temperature) at a rate of about 10 K/min and maintaining the porous support for about 2 hours to about 10 hours under the temperature and a pressure of about 100 mm Hg or less, with the liquid nitrogen of which the relative pressure (P/P0) is adjusted to about 0.01 torr or less being adsorbed by the porous support at about 32 points to the relative pressure of 0.01 torr to about 0.955 torr and desorbed at about 24 points to the relative pressure of about 0.14 torr. Given the volume of the porous support, from the amount of Nmeasured by the above method the porosity may be obtained.

In another embodiment, each porosity of the micropores, mesopores, or macro pores, and the entire porosity of the porous support may be measured by the Nabsorption isotherm through the BJH method using the pore measurement device (ASAP2020, available from Micromeritics Instrument Corporation).

The negative active material according to embodiments is positioned in the pores of the porous support. Thus, the volume expansion of the silicon during charging and discharging may be effectively suppressed and high capacity of silicon may be obtained.

In one or more embodiments, the silicon-including porous support may include nano silicon or SiO(0≤x≤2). This silicon-including porous support may provide for more uniformly deposited silicon in the pores as compared to the carbon-included porous support. Thus, smaller sized silicon may be deposited in the pores of the porous support. This enables more effective suppression of volume expansion of the silicon.

The porous support may be, based on 100 wt % of the negative active material, about 30 wt % to about 70 wt %, about 35 wt % to about 65 wt %, or about 40 wt % to about 60 wt %. If the porous support satisfies in these ranges, the amount of silicon to be deposited may be controlled, and, thus, the desired capacity may be secured.

The negative active material according to embodiments includes a carbon layer between the silicon layer positioned in the pores and the pores. Thus, enhanced ionic conductivity may be achieved.

In embodiments, the carbon layer may include amorphous carbon. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, sintered coke, or combinations thereof.

In one or more embodiments, a thickness of the carbon layer may be about 1 nm to about 15 nm, about 1 nm to about 10 nm, or about 1 nm to about 5 nm. If the thickness of the carbon layer is within these ranges, the ionic conductivity may be enhanced and rate characteristics and cycle-life characteristics may be improved.

The silicon layer may include amorphous silicon. If silicon included in the silicon layer is amorphous silicon, volume expansion may be reduced during charging and discharging relative to crystalline silicon, and cycle-life characteristic also may be enhanced. In embodiments, the amorphous Si may be confirmed by measuring using TEM or XRD. In case of measuring using TEM, silicon exhibiting no crystal lattice stripes may be indicative of amorphous silicon. In case of measuring an XRD using a CuKα ray as a target ray, an appearance of broad peak may be indicative of amorphous silicon.

The silicon positioned in the pores may be elemental Si or a pure Si.

In one or more embodiments, an amount of the silicon may be, about 100 wt % of the negative active material, about 40 wt % to about 80 wt %, about 45 wt % to about 65 wt %, or about 50 wt % to about 60 wt %. If the amount of silicon is within these ranges, higher efficiency and capacity may be exhibited, and cycle-life characteristics may be excellent.

The negative active material according to one or more embodiments includes amorphous carbon positioned on the core. For example, the negative active material may include an amorphous carbon layer surrounding the outer surface of the core. The amorphous carbon layer may completely surround the surface of the core or may partially surround the surface of the core. A thickness of the amorphous carbon layer may be about 1 nm to about 100 nm, about 1 nm to about 50 nm, or about 1 nm to about 30 nm. If the thickness of the amorphous carbon layer is within these ranges, irreversible reactions may be minimized and the resistance may be enhanced.

In the amorphous carbon layer, the amorphous carbon may be pitch carbon, soft carbon, hard carbon, mesophase pitch carbide, sintered coke, carbon fiber, or combinations thereof.

Thickness of the amorphous carbon layer indicates a thickness of the amorphous carbon on the outer surface of the core, and if amorphous carbon is unevenly located, it may be a length at the thickest point. In one or more embodiments, the thickness may be an average thickness. If the thickness of the amorphous carbon coating layer is within the above-noted ranges, irreversible capacity loss may be reduced, charge and discharge efficiency may be enhanced, and rate characteristic may be enhanced.

According to embodiments, the amount of carbon may be about 1 wt % to about 30 wt %, about 1 wt % to about 20 wt %, or about 1 wt % to about 15 wt % based on 100 wt % of the negative active material. An amount of the carbon represents the sum of amounts of carbon in the carbon layer positioned in the pores and the amorphous carbon layer positioned on the core. In one or more embodiments, the entire carbon included in the negative active material is significant, and there is no need to define the amount of the carbon included in the carbon layer and the amount of the carbon included in the amorphous carbon layer.

If the amount of carbon included in the negative active material is within the above ranges, conductivity may be enhanced, thereby maximizing capacity.

In embodiments, silicon carbide may be positioned between the carbon layer and the silicon layer. In the negative active material according to one or more embodiments, the presence of the silicon carbide between the carbon layer and the silicon layer may be confirmed by X-ray diffraction. Since the silicon carbide is positioned between the carbon layer and the silicon layer, a boundary between the carbon layer and the silicon layer may be clearly identified.

A negative active material according to another embodiment includes secondary particles where at least one primary particle is agglomerated. The primary particle includes a core including a porous support including pores, a carbon layer positioned in the pores, a silicon layer positioned on the carbon layer, and an amorphous carbon layer positioned on the outer surface of the core. The pores may include mesopores and the mesopores may be about 50% to about 100%, about 60% to about 100%, or about 70% to about 100%, based on the entire porosity.

For better comprehension and ease of description, the above-described negative active material according to one embodiment refers as a negative active material according to the first embodiment and a negative active material according to another embodiment refers to a negative active material according to the second embodiment.